Due to the need of starting a lamp, some conventional lamp holders are provided with ballasts, and an output terminal of the lamp holder is coupled to the line wire of mains electricity by the ballast. With the development of lighting technologies, some lamps are set up with electronic circuits inside, therefore they can be directly coupled to the mains electricity. However, lamps with electronic driver circuits generally cannot withstand high input voltage. With the ballasts set inside the conventional lamp holders, if the lamp with electronic driver circuit is directly installed on the conventional lamp holder, when turned on, the lamp with electronic driver circuit might be subjected to excessive voltage due to the effect of the ballast, and the electronic driver circuit inside the lamp might be damaged. Due to the lack of electrical knowledge and operation ability, ordinary users are not qualified for modifying the conventional lamp holders to make them compatible with ballasts.